On Wednesday evening, SpaceX will launch the first all-crew spacecraft into Earth's orbit, putting to a conclusion a summer of private spaceflight with one of the most daring tourist ventures ever tried.
Climate conditions are good, with an 80 per cent possibility of launch, about official forecasters, and a five-hour launch window for "Inspiration4" opens at 8:02 p.m. (0002 GMT Thursday).
The crew piled into white Teslas to applaud from a modest crowd under bright skies following a tour from SpaceX CEO Elon Musk and drove to the site where they will wear their spacesuits.
A Falcon 9 rocket with a Dragon capsule on top will blast off from NASA's Kennedy Space Center at Florida's famed launch complex 39A, where the Apollo 11 mission previously set out for the Moon.
The trajectory of the spaceship will take 357 miles (575 kilometres) into space, which is more than twice as far as the International Space Station (ISS).
The four-person crew, all of whom are Americans, will land down off the Florida coast completing three days in orbit.
Before the flight, NASA Administrator Bill Nelson tweeted, "The #Inspiration4 launch shows us of what can be accomplished when we engage with private enterprise!"
- Strenuous workout -
Hayley Arceneaux, a 29-year-old physician assistant, is a paediatric cancer survivor. She'll be the first person to go into orbit with a prosthesis on a part of her femur and the youngest American to do it.
Chris Sembroski, 42, is an aviation data engineer who served in the United States Air Force.
In 2009, Sian Proctor, a 51-year-old geoscientist and instructor, came close to becoming a NASA astronaut.
She will be the fourth African-American woman to travel to the moon.
They connected over six months of preparation, which comprised climbing Mount Rainier, high G-force conditioning, and a helical flight that gave them a taste of weightlessness.
The goal of the project is to raise $200 million for St Jude's Children's Research Hospital, a renowned Tennessee hospital. Arceneaux was treated there when he was a youngster, and today he works there.
The team will bring with them a ukulele, 66 pounds (30 kilogrammes) of hops for brewing space beer, and numerous non-fungible tokens, which will be auctioned off to raise money for the purpose.
Biological data like heart rate and sleep, as well as cognitive abilities, will be examined during the journey to investigate the health effects of space travel.
The Dragon will include a cupola observation dome - the world's largest space window — for the first time to take in the view. The dome will take the place of the Dragon's traditional locking mechanism with the International Space Station.
- Space privatisation -
Aside from the philanthropic and scientific components, the mission's declared objective is to mark a watershed moment in the democratisation of space by demonstrating that the cosmos is available to individuals who have not been hand-picked and groomed for long as astronauts.
For SpaceX, this is only the first step toward founder and CEO Elon Musk's ultimate goal of multi-planetary mankind.
Although the mission should be entirely automated, SpaceX has prepared the crew to take control in emergencies.
The space journey comes after a summer that has seen billionaires Richard Branson and Jeff Bezos duke it out to reach the last frontier.
Branson, the creator of Virgin Galactic, was the first to accomplish the accomplishment on July 11, followed by the CEO of Blue Origin nine days later.
This will be SpaceX's fourth crewed trip, with the company having already transported ten men to the International Space Station for NASA.